One-step light-induced hierarchical surface wrinkles on photodegradable polymer films

Photodegradable polymers have become an emerging class of stimulus-sensitive materials for advanced applications, in which using the photolysis characteristic for patterning surface is a key but still a notable challenge. Herein, we report a simple, facile, green and high-efficiency strategy to induce and further tune surface wrinkling only relying on one-step ultraviolet (UV) irradiation of a photodegradable polymer-based film/substrate composite system. Interestingly, a series of intriguing wrinkling states from no wrinkling to surface wrinkling and final no wrinkling with UV exposure take place on the photodegradable polymer film. This wrinkling behavior is intimately related to the competition between the stress accumulation from the heating effect of UV lamp itself and the stress release from the UV-induced molecular chain breakage. Meanwhile, the dependence of photo- degradable polymer film modulus and photodegradation-induced stress release on the exposure time has been characterized by taking advantage of surface wrinkling metrology, which is not easily accessible to other systems and methods. This one-step light irradiation strategy has enabled the fabrication of diverse hierarchical surface wrinkling on photodegradable polymer film by simply controlling the UV exposure time. As demonstrated, these hierarchical surface wrinkles with tunable features have been applied for optical information display/storage and optical gratings. Notably, this simple flexible light control strategy not only provides new insights into the photo- induced change in mechanical properties and stress release of photodegradable polymers in molecular level, but also paves new avenues for advanced wrinkle-based applications by incorporating desirable functional materials into the photodegradable polymer-based systems.